New Insights into the Cleaning of Paintings

Sensitivity of Oil Paint Surfaces
to Aqueous and Other Solvents
Hannah Tempest, Aviva Burnstock, Polly Saltmarsh,
and Klaas Jan van den Berg
Abstract. This paper investigates the sensitivity of modern commercially produced artists’ oil
paints to the use of aqueous and other solvents for cleaning. Water sensitivity has been observed in
oil paintings where the paint has been used to create a great range of surface effects. It was reported
in paint that exhibits efflorescence where fluctuations in environmental conditions or former treatments
may have accelerated migration of degraded components to the surface of the paint film.
The colored passages most frequently cited as problematic included ultramarine, cadmium yellows,
chromium oxide green, and cobalt violet. Oil paint films, based on twentieth- century manufactured
paints, with known proportions of pigments, stearates, aluminum hydroxide, hydrolyzed linseed
oil, and hydrogenated castor oil in linseed oil were prepared and cured. After artificial aging, the
paints were tested for water sensitivity. Ultramarine paints were the most sensitive to water applied
by swab, followed by chromium oxide, whereas raw sienna was the least sensitive. The inclusion
of linseed fatty acids and aluminum hydroxide increased the sensitivity of the paints to water. Aluminum
stearate- containing paints swabbed with aqueous solvents exhibited localized stearic acid
efflorescence. Ultramarine stearate- containing paints formed a paint- medium skin that was initially
resistant to swabbing with water but contained water- sensitive paint beneath.
INTRODUCTION
Hannah Tempest, National Gallery of Denmark,
Sølvgade 48- 50, DK- 1307 Copenhagen, Denmark.
Aviva Burnstock, Department of Conservation
and Technology, Courtauld Institute of Art,
Somerset House, Strand, London WC2R 0RN,
UK. Polly Saltmarsh, London, UK. Klaas Jan van
den Berg, Netherlands Cultural Heritage Agency,
P.O. Box 76709, 1070 KA Amsterdam, Netherlands.
Correspondence: Aviva Burnstock, aviva
.burnstock@courtauld.ac.uk; Klaas Jan van den
Berg, k.van.den.berg@cultureelerfgoed.nl. Manuscript
received 19 November 2010; accepted 24
August 2012.
The water sensitivity of modern paintings produced with commercial artists’ oil
paints is a phenomenon commonly encountered by conservators of twentieth- century
paintings. Sensitivity to the use of aqueous and other solvents typically applied with a
cotton wool swab during cleaning affects well- bound oil paint and can also occur in paint
that has been applied straight from the tube, with no modifications, or in tube paints
with artists’ additions of materials such as non- or semidrying oils, waxes, or resins. The
problem has been reported in passages of large, unvarnished, and unglazed modern oil
painting, including Jasper Johns’ Untitled, 1964–1965 (Stedelijk Museum, Amsterdam;
Burnstock et al., 2007; Wijnberg et al., 2007), Karel Appel’s Les Animaux, 1961 (Collection
of the Netherlands Institute for Cultural Heritage [ICN]; Mills, 2008; Mills et al.,
2008), and paintings by Robyn Denny, dating from the 1960s, at the Museu Calouste
Gulbenkian, Lisbon (Gayler et al., 2008). Related case studies and technical analysis of
water- sensitive oil paintings from the 1950s and 1960s are discussed in depth in a recent
Courtauld Institute of Art student project (Tempest, 2009).
Dirt deposition may be patchy or even and can be particularly disfiguring on modern
paintings, which may have no layer of protective varnish, a varied surface texture, different
degrees of porosity in different areas, or a significant degree of impasto to trap surface